The long-range goal of this application is to study the structure and function of several periplasmic binding or receptor proteins. These proteins are essential components of osmotic shock-sensitive active transport and chemotaxis in bacteria. X-ray crystallography will be used primarily to ahcieve this goal. This goal is imminently possible since we have obtained single crystals of five receptor proteins specific for arabinose-, D-galactose-, maltose-, leucine/isoleucine/valine-, and sulfate-binding proteins. Furthermore, the crystal structure of the arabinose-binding protein has been solved at 2.4. A resolution and the analysis of other binding proteins are already in progress. The same technique will be utilized to determine in detail the stereochemistry of ligand binding to these binding proteins. Conformational changes attendant to binding, postulated to be essential in translocation and an obligatory first step in transmission of signals during chemotactic behavior, can be elucidated in dtail by this analysis. We will also employ stopped-flow rapid mixing and small angle x-ray scattering techniques to further study the liganded state of the various receptor proteins. Results of this study will from a major basis for a molecular understanding of the role of binding proteins in transport and chemotaxis, two important cellular processes. Transport processes perform a vital function in the life of the cell by maintaining a relative constancy of the environment within the cell and regulating the entrance and exist of various substances necessary for metabolic activity. In addition, chemotaxis is important for the survival of the microorgnisms since interaction with the environment depends largely on the ability to respond to stimuli. Taxis of cells from higher organisms is important for fertilization and biological defense mechanisms. Further, the principle of single processing and transmission of information in bacteria is similar in a wide variety of sensory systems. Therefore, detailed understanding of these processes in a relatively simple system will allow evaluation of similar process and principles in higher organisms.